C0604: Active Air Dam Control Circuit Performance
What to do
Kneel down and look under the front bumper before you drive over anything.
Your car has a panel that lowers at speed for aerodynamics and retracts so it clears kerbs and ramps. This code means it is not moving where it is told — and if it is stuck in the lowered position, the next steep driveway or car park ramp will take it off.
If it is hanging down, take ramps and kerbs slowly and at an angle until it is repaired.
The cause is usually mechanical rather than electrical — something jamming the travel, a bent linkage from a kerb strike, or packed ice and road debris. Mention if the car has grounded on anything, or been driven in deep snow or mud.
Nothing else about the car is affected; it drives normally and this is one to book in rather than worry about.
What this code means
The active air dam is not performing as commanded.
An active air dam is the panel that lowers below the front bumper at speed to reduce drag, and retracts at low speed so the car can clear kerbs and ramps.
This code is the performance version rather than a communication fault — the module commanded a movement and measured a result that did not match. The panel is not going where it is told, which usually means the mechanism rather than the electronics: a motor straining against an obstruction, a linkage bent by a kerb strike, or ice and packed debris jamming the travel.
The consequence worth acting on is a dam stuck down. A panel deployed at parking speed meets the first steep driveway or car park ramp, and it is the cheapest part on the car to destroy expensively.
Look under the front bumper. If a panel is hanging below the bodywork, treat ramps and kerbs carefully until it is fixed. It costs nothing to check and it is the whole of what a driver can usefully do here.
The corpus carries the communication version of this fault at U0645 — a module that has gone silent rather than one that is trying and failing.
Why this page exists when its neighbours do not. Nothing in the public web documents this block — four independent searches established that on 2026-08-10. This code is written because a manufacturer named it, with its definition, in a technical service bulletin filed with the US road safety regulator, and that OEM wording agrees with the standard's own enumeration. Its neighbours have no such document, so they remain undocumented rather than guessed.
Likely causes
Start here
- Physical damage from road debris · moderate
- Corroded or loose connector · easy
Less common
- Water ingress into connector · moderate
- Damaged actuator linkage · moderate
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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